HOW DISCOVERIES ARE MADE 117 



strain, fear that it may part, or that some hasty move- 

 ment may lose him his fish. 



Most discoverers are like fishers for sprats : they go 

 where they are sure of a reward ; but the gain is not 

 great, at least as regards sport. It is much more fun to 

 fish for salmon ; but then there is a great chance that the 

 angler has mistaken the place to fish, or that he has used 

 the wrong fly ; or that the weather is unfavourable ; or 

 that a hundred things, impossible to foresee, will prevent 

 the salmon taking the hook. 



We may not pursue the allegory further: salmon are 

 now not nearly so plentiful a$ they used to be; sprats, 

 perhaps even more numerous. And it requires training 

 and a good eye to know where the salmon lie and in what 

 pools to fish. 



But let us dismiss this image and become historical. 



One of the first puzzles which awaited solution was the 

 nature of flame. The ancients believed it to be an ele- 

 ment that is, a property, or perhaps a constituent of 

 most, or of all, other things. Flame, said they, is hot; 

 and everything which is hot partakes of the nature of 

 flame. 



Robert Boyle guessed that it was a sign of the rapid 

 movement of the minute particles of which he supposed 

 everything to be composed ; but this, although very near 

 what we now suppose to be the truth, was merely a lucky 

 guess ; for he had no real ground for making the sugges- 

 tion. It was noticed that flame appears when anything 

 burns; and the reason for combustion, or burning, had 

 first to be sought. 



The real step towards this was made by Joseph Priestley, 

 an English dissenting minister, and by Karl Scheele, a 

 Swedish apothecary, almost at the same time. Priestley 

 was a fisher for salmon, to revert to our old image ; he 

 fished everywhere and caught many large fish. And so 



\ 



